Web tension control system



Aug. 14, 1962 c. E. JORDAN ETAL WEB TENSION CONTROL SYSTEM 3Sheets-Sheet 1 Filed July 27, 1959 muBOm Q n a 0 ma ON \N\ MN m&

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ATTORNEYS Aug. 14, c E. JORDAN ETAL WEB TENSION CONTROL SYSTEM FiledJuly 27, 1959 3 Sheets-Sheet 2 S 8 S B R N P. F- 3 m "6.25; h m A a N5&3 a 2523i m w H m W m0. o 3 V o m T M258 9 n w. w w M D mm u m R H kwM m (l C R W N 0 E mos: -25 QZEME j f mm 3,049,313 WEB TENE'aION CGNTROLSYSTEM Charles Edward Jordan, Milwaukee, Wis, and Richard W. Phelps,Fulton, N.Y., assignors to The Black-Clawson Company, Hamilton, Ohio, acorporation of Ohio Filed July 27, 1959, Ser. No. 829,828 9 Claims. (Cl.24275.44)

This invention relates to a control system for regulating the tension ina moving web of sheet material.

Sheet material, such as paper, plastic film, foil, and the like isusually manufactured and supplied in large rolls. In the preparation forultimate use, the material is taken as a web from the original rollthrough one or more forms of converting machinery, where it may beslitted, coated, laminated, or otherwise converted, and then rewound.During the unwinding and rewinding, it is desirable that a constantgiven tension be maintained within the moving web to prevent thebreaking of the web and to assure a uniform surface speed according tothe requirements of the converting processes involved.

This invention provides an automatic constant tension control systemwhich eliminates any necessity for contacting the moving web between anunwind stand and a motor driven winder. The load on the winding motor ismeasured as an indication of the tension in the web and is compared toan adjustable standard representing the desired load. The compareddifference between the standard and the actual load is applied to aservo amplifier for increasing or decreasing the drag of an adjustablefriction brake on the unwind stand in such a direction as to bring themotor load into coincidence with the standard.

The system of this invention includes operators controls for theselection of the tension which the system will automatically maintain,as described. Provision is also made for independently setting in astarting breakaway tension which may be ditferent from that set in forcontinuous running. The system includes a time delay to provide time forthe winder to come up to speed on the presetting break-away tension withautomatic transfer to automatic control. Also, the operator may at anytime switch to fully manual control through which he may remotelyincrease or decrease the tension at will.

A principal object of this invention is to provide a tension regulatingsystem as outlined above for the automatic control of tension in amoving web of sheet material, such as paper.

A further object of this invention is to provide a tension controlsystem as outlined above through which the tension of a moving web ofsheet material may be held at a preselected value.

Another object of this invention is to provide an automatic tensionregulating system as outlined above wherein an adjustable brake on anunwind system may be varied either manually or controlled automaticallythrough the system.

Another object of this invention is the provision of a closed looptension regulating system as outlined above which continuously comparesthe load of a winder motor against a reference representing the desiredload and controls an adjustable brake on an unwind stand according tothe difference between the actual and desired loads. A rate network isincluded to improve accuracy and response.

A still further object of this invention is the provision of a constanttension control system as outlined above which operates without thenecessity of contacting the surface of the moving web of paper.

Other objects and advantages of the invention will be apparent from thefollowing description, the accompanying drawings and the appendedclaims.

In the drawings- FIG. 1 is a perspective view of the system of thisinvention as applied to a slitter-rewinder, a portion of the systembeing diagrammatically shown for the purpose of illustration;

'FIG. 2 is a schematic of the air supply system; and

FIGS. 3, 4 and 5 are electrical schematic diagrams of the control systemof this invention with FIG. 3 representing the power supply, FIG. 4representing the refererence voltage supply and the input to the servoamplifier including the ditferentiator, and FIG. 5 representing theservo amplifier and its interconnected relation to the operatorscontrols.

Referring to the drawings, which illustrate a preferred embodiment ofthe invention, an unwind stand is indicated generally at 10 as rotatablysupporting a roll 11 of sheet material, such as paper. The material ofthe roll 11 is shown as being drawn as a web 12 into a converterconsisting of a slitter-rewinder 13 which includes a mandrel 14 uponwhich the web 12 is rewound after being processed therein. The rewindermandrel 14 is driven to rewind the web 12 through the winder drum 15 byan electric rewind motor 16 which causes the Web 12' to be drawn fromthe supply roll 11 through the slitting apparatus contained within theslitter-rewinder 13 and wound onto the mandrel 14 in the converted stateto form the new roll 17 on the mandrel 14.

The unwind stand lit includes adjustable friction means for causing adrag which resists the unwinding of the roll 11 by the motor 16. Thisdrag is transmitted to the motor 16 by means of tension through the web12. The friction means preferably consists of an air actuated brake 20,which may be of any conventional type capable of causing a drag inresponse to the pressure of an air signal applied thereto. A source ofair under pressure, indicated at 21 in FIGS. 1 and 2, supplies air forthe operation of the brake 20 through a valve arrangement including ahand valve 22 and an electric solenoid valve 23. A gage 24 may beprovided for the purpose of indicating the operative pressure at thebrake 20.

Means for varying the amount of air pressure applied from the source 21to the brake 24 to vary the braking effort and the tension applied bythe brake 20 to the web 12 includes a motor-positionable air pressurecontrol valve indicated generally at 25. The valve 25 includes acontrollable pressure regulator valve body 26 connected between thesource 21 and the solenoid valve 23 and an example of a commerciallyavailable valve of this description is the Model H3 of the WestinghouseAir Brake Company of Wilmerding, Pennsylvania, sold under the trade nameof Controlair. A reversible electric drive motor 27 is mounted in directdriven relation to the valve body 26 for causing the body 26 to increaseor decrease the pressure applied to the brake 20 according to therequirements of the system of this invention. The drive motor 27 mayconsist of one of the common class of reversible electric motorscharacterized by modest power requirements and negligible overrunsuitable for control by a servo amplifier. An example of one suchsuitable motor for this purpose is the Model SM1O of the Jordan Company,Inc. of Milwaukee, Wisconsin, sold under the trade name of Valvetrol.

Means for regulating the control valve 25 includes the electricalcircuit components of FIGS. 3-5, most ofwhich are contained within acontrol box indicated somewhat diagrammatically at 30 in FIG. 1. The box30 includes a control panel 31 upon which is mounted the controls bywhich the system is regulated by an operator. The panel 31 includes asolenoid on-ofr switch 33 connected as shown in FIG. 2, to control thesolenoid valve 23 for controlling the admission of the air from thevalve 25 to the brake 20. A function selector switch 35, designated asHand-Auto, provides for the selection of it? either manual or fullyautomatic tension control. The panel 31 also includes an Increase pushbutton 36 and a Decrease push button 37 by means of which an operatorcan manually effect an increase or decrease in the air pressure at thebrake 20 to vary the tension in the web 12. The buttons 36 and 37 arealso operable to establish a break-away tension in the web 12 prior tothe starting of the rewinder motor 16 in either position of the Hand-Auto switch 35.

Means on the panel 31 for setting in a desired tension for automaticmaintenance includes a Load Set dial 40. The dial 40 may be positionedaccording to the experience of an operator at given positioncorresponding to a given tension within the limits which can bemaintained by the system, and this tension will be maintained throughoutthe operation of the slitter rewind 14. The control box 30 includes timedelay means for effecting a transfer from the break-away tension as setin by the buttons 36 and 37 to the constant tension as set in by theLoad Set dial 40.

Not all of the system components can conveniently be located on orwithin the control box 30, and in addition to an external 115 volt, 60cycle power source indicated generally at 42, a motor load signalpick-up means in the form of a current transducer 43 is positioned inthe power leads to the rewind motor 16. The current transducer 43measures the load on the motor 16 as an indication of the tension in theweb 12. The transducer 43 may consist of a calibrated shunt for DC.rewind motors, and a rectifying current transformer in the case of anA.C. motor, to provide a DC. electric signal proportional to the motorload.

Referring now to the wiring diagrams of FIGS. 3-5, and considering themas a whole, it will be seen that an electric circuit is provided whichtakes the signal from the current transducer 43 and compares it with areference signal set in by the Load Set dial 40 to provide an outputsignal for the control of the air control valve 25. A primary powersupply for the system is shown in FIG. 3 as including a powertransformer 45 with a primary 46 connected to the 115 volt 60 c.p.s.reference source 42. A high voltage secondary 47 provides a plurality ofisolated rectified high voltage sources, indicated as B+1, B+2 and B+3,through one half of a dual triode 50, connected here as a diode, and acommon R-C filter-decoupling network 51. The voltages B+1, B+2 and B+3are employed by the servo amplifier portion of the system shown in thewiring diagram of FIG. 5. The power transformer 45 also includes a lowvoltage secondary 52 for the purpose of supplying a volts D.C. through aselenium rectifier 53, with a filter capacitor 54 and load resistor 55.The --5 volts D.C. supply is also employed by the circuit components ofFIG. 5. A common fila- Inent winding 56 supplies 6.3 volts A.C. asrequired by the components of the circuit.

Referring now to FIG. 4, means for provinding a variable referencesignal representing a desired tension in the Web 12 includes a step-downtransformer 60 having a primary connected to the source 42. A pair ofdiodes 61 are connected to the secondary of the transformer 60 for fullwave rectification through a R-C filter network 62. Accurate voltageregulation is maintained by a zener diode 63 connected across the outputof the network 62. A Load Set potentiometer 65, connected for mechanicalmovementwith the dial 40, is electrically connected in series with anadjustable rheostat 66 and, in turn, connected in parallel with thediode 63.

The output of the Load Set potentiometer 65 is a low level regulated DC.signal representing a desired motor 16 load, and this signal is appliedpast adecoupling capacitor 68 to one leg of a stabilizing circuitconsisting of a partial differentiating network 70. A second input tothe network 70 comprises the motor load signal from the currenttransducer 43 which is fed to the network 70 through a shielded lead-incable 72. The network 70 partially differentiates the input signal fromthe transducer 43 to supply a voltage having a component proportional tothe motor 16 load and another component proportional to the rate ofchange of the motor load. The network includes a rate adjustpotentiometer for adjusting the ratio of the rate signal as compared tothe motor load signal, the purpose of which is to provide compensa tionfor various time lags in the system. This signal is then compared to theapplied reference voltage from the Load Set potentiometer 65 and thedifference therebetween is applied to the armature of a synchronousvibrator S1. The alternately selected contacts 31. and 83 of thevibrator 81 are connected to the opposite ends of the primary of acoupling transformer 85.

The purpose of the synchronous vibrator 81 and the transformer 85 is toprovide an A.C. signal having a magnitude proportional to the differencebetween the partially differentiated motor signal and the referencevoltage, and either in phase with the reference supply 42 or 180out-of-phase therewith, depending upon whether the motor load signal isgreater than or less than the reference voltage. The secondary of thetransformer 85 is connected to the grid of the first of a pair ofseriesconnected common amplifier stages 36 and 87 each associated with adual triode tube 88 of FIG. 5. It may be noted that the voltages B+1 and8+2 are used here for the purpose of supplying plate voltage to thesections of the tube 88.

A third amplifier stage includes the second half of the dual triode 50,the grid of which is connected to the preceding stage through a variablegain potentiometer 91. The potentiometer 91 forms the means by which thegain of the servo amplifier of FIG. 5 may be controlled and adjusted tomeet the requirements of a given installation.

The system includes delay means by which the preselected tension on thedial 40 is held from being applied through the circuit to the brake 20until the motor 16 is started and the web 12 is brought up to operatingspeed. This has the effect of delaying the application of automaticcontrol until after the surge of starting current is past. The delaymeans includes a time delay relay 95 having an armature actuating coil96 connected for energization through a switch 97. The switch 97 ispreferably an integral part of the starting switch for the motor 16 tobe closed at the same time that the motor 16 is started.

The relay 95 is adjusted to close a pair of normally open contacts 98approximately 30 seconds after the closing of the switch 97. The closingof the contacts 98 applies the B+3 voltage to the plate of the tube 50.The relay 95 includes a set of normally closed contacts 100 throughwhich the tension may be adjusted by means of the push buttons 36 and 37prior to the starting of the motor 16.

The output of the tube 50, comprising the now considerably amplifiedsignal from the transformer 85, is applied equally to each of thecontrol grids of a pair of thyratrons and 106. The grids of thethyratrons are normally biased to cut off by the -5 volts D.C. from thepower supply transformer 45. The plates of each of the thyratrons areconnected to ground through the secondaries 108 of a pair of identicalsaturable transformers 110 and 111. The primaries 112 of thetransformers 110 and 111 are, in turn, energized from the referencesource 42 of 115 volts A.C. through an autotransformer 115. Thethyratrons 105 and 106 are therefore respectively energized from thesource 42 through the transformers 110 and 111. However, the voltageacross the thyratron 105 is out-of-phase with that at the thyratron 106,as indicated by the conventional dots on the transformers 110 and 111indicating the instantaneous polarity.

It will therefore be seen that any given A.C. signal output from thetube 50, if of sufiicient magnitude, will fire only one of thethyratrons depending upon the phase of the signal, that is, dependingupon whether an increase or decrease in tension is required. The firingof one of the thyratrons 105, 106 saturates its associated transformer110 or 111, greatly reducing its reactive impedance.

The reversible motor 27 of the valve has one of its inputs 120 connectedfor energization from the autotransformer 115 through the primary 112 ofthe transformer 110 and has its other input 121 connected forenergization through the primary 112 of the transformer 111. Theconduction of the thyratrons, due to the presence of an amplifieddifference signal, will necessarily be for half cycles only of the powersource 42. This however is sufficient to saturate the associatedtransformer 110 or 111 and the transformer which remains substantiallysaturated during the non-conducting half cycle, thereby providing forthe application of the power from the autotransformer 115 to theappropriate motor 27 input. The purpose of the autotransformer 115 is toovercome the IR drop within the saturable transformers 110 and 111.

The Hand-Auto switch 35 operates in the Auto position to connect thecathodes of the thyratrons 165 and 106 to ground. In the Hand position,the servo amplifier of FIG. 5 is disabled. However, this positionapplies the power source 42 to the Increase and Decrease push buttons 36and 37. The push buttons 36 and 37 are connected to apply the source 42directly to the appropriate motor 27 input 120 or 121 to effect anincrease or a decrease of the air supply to the brake 20 as long as thebutton is depressed. Releasing the button breaks the circuit to themotor 27. The normally closed contacts 100 on the relay 95 also serve toapply the source 42 to the buttons 36 and 37 so that the tension may beregulated prior to starting the motor 16 regardless of the position ofthe Hand-Auto switch 35.

The operation of this invention is largely self-evident from theforegoing description. It will be seen that the tension may be eitherincreased or decreased by the approp-riate operation of the push buttons36 and 37 prior to the starting of the rewind motor 16, and during theoperation of the reWinder 13 by placing the switch 35 in the Handposition. However, the Auto position is normally employed for thepurpose of maintaining a given tension in the web 12 according to thesetting of the Load Set dial 40. Any variation from the setting as thusspecified causes a difference signal to be applied to the thyratrons 105and 106 to effect corrective action by either increasing or decreasingthe air pressure at the brake 20 through the control valve 25. It willtherefore be seen that a fully automatic and versatile tensionregulating system is provided which eliminates guesswork and affordsuniform tension control throughout the entire conversion of a web undercircumstances where a control of tension is desired.

While the form of apparatus herein described constitutes a preferredembodiment of the invention, it is to be understood that the inventionis not limited to this precise form of apparatus, andthat changes may bemade therein without departing from the scope of the invention which isdefined in the appended claims.

What is claimed is:

1. A constant tension regulator for a moving web from an unwind rollonto a motor driven winder roll, comprising a variable brake on saidunwind roll for determining the tension in said web, means providing asignal in proportion to the motor load on said Winder roll representingthe actual tension in said web, means providing a reference signalproportional to a desired motor load representing a desired web tension,means for comparing said motor signal and said reference signal andproviding an output signal in response to the difference between theactual and the desired tension, and servo means respon sive to saidoutput signal for varying said brake in such a manner as to tend toequalize said motor signal and said reference signal.

2. A continuous closed loop system for regulating the tension in amoving web from an unwind roll to a winder roll driven by a motor,comprising controllable drag brake means on said unwind roll, means formeasuring the load on said winder motor for providing an electric signalrepresenting said load, means providing a variable standard referencesignal representing a desired motor load, continuous signal comparisonmeans for comparing said reference signal with said motor load signaland providing an output signal representative of the differencetherebetween, and reversible servo follow-up means responsive to saidoutput signal connected to control said drag means to modify the drag onsaid unwind roll to equalize said reference signal and said load signal.

3. A constant tension regulator for a moving WCb from an unwind rollonto a motor driven winder roll, comprising a variable brake on saidunwind roll for determining the tension in said web, means providing asignal in proportion to the motor load on said winder roll, a manuallyvariable reference signal generating means providing a reference signalproportional to a desired motor load representing a desired web tension,means for comparing said motor signal and said reference signal andproviding an output signal in response to the difference therebetween,and servo means responsive to said output signal for varying said brakein such a manner as to tend to equalize said motor signal and saidreference signal.

4. A constant tension regulator for a moving web from an unwind rollonto a motor driven winder roll, comprising a variable brake on saidunwind roll for determining the tension in said web, means providing asignal in proportion to the motor load on said winder roll, meansproviding a reference signal proportional to a desired motor loadrepresenting a desired web tension, circuit means for comparing saidmotor signal and said reference signal and providing a differencesignal, differentiating means for providing an output signal having afactor representative of the rate of change of said difference signal,and servo means responsive to said output signal for varying said brakein such a manner as to tend to equalize said motor signal and saidreference signal.

5. A constant tension regulator for a moving web of paper from an unwindroll onto a motor driven winder roll, comprising a variable brake onsaid unwind roll for determining the tension in said web, meansproviding a signal in proportion to the motor load on said winder roll,a manually controlled reference signal proportional to a desired motorload representing a desired Web tension, means for comparing said motorsignal and said reference signal and providing an output signal inresponse to the difference therebetween, servo means responsive to saidoutput signal for varying said brake in such a manner as to tend toequalize said motor signal and said reference signal, and manuallyoperable circuit means connected to said servo means for changing saidtension independently of said reference signal.

6. A device for regulating the tension in a moving web of paper from anunwind roll to a winder roll driven by a motor comprising an air brakeon said unwind roll, a source of air under pressure, a variable airvalve connecting said source and said brake for varying the air pressureapplied to said brake from said source, means responsive to the load onsaid winder motor for supplying an electric signal in proportion to saidmotor load, means providing a variable reference signal representing adesired tension in said web, circuit means for comparing said referencesignal and said motor load signal and providing an output signalproportional to the difference there between, means for differentiatingsaid output signal to provide an indication of the rate of change ofsaid load, and reversible servo means connected to operate said variableair valve and responsive to said differentiated signal to cause said airbrake to modify said unwind tension to tend to equalize said motorsignal and said reference signal.

7. A constant tension regulator system for a moving web from an unwindroll onto a motor driven Winder roll, comprising a variable brake onsaid unwind roll for determining the tension in said web, meansproviding a signal in proportion to the motor load on said winder roll,means providing a reference signal proportional to a desired motor loadrepresenting a desired web tension, circuit means for comparing saidmotor signal and said reference signal and providing a differencesignal, adjustable means for compensating for system delays including amanually variable differentiating means for providing an output signalhaving an adjustable factor representative of the rate of change of saiddifference signal, and servo means responsive to said output signal forvarying said brake in such a manner as to tend to equalize said motorsignal and said reference signal.

8. A constant tension regulator system for controlling the tension in amoving web from an unwind roll onto a motor driven Winder roll,comprising variable brake means on said unwind roll for creating tensionin said web, controllable valve means connected to control said variablebrake means, a control circuit for operating said valve means includingmeans for measuring the load on said winder and providing a signalindicative of the tension in said web, automatic control means connectedto receive said signal from said load measuring means for controllingsaid valve means, manual circuit means separate from said automaticcontrol means for presetting a desired starting tension in said Webthrough said valve means, and trans fer means for transferring controlfrom said manual means to said automatic means in response to thestarting of said winder including a delay relay having one set ofcontacts in said manual circuit means and having a further set ofcontacts operable upon the closing of said relay to activate saidautomatic control means.

9. A tension regulating system for controlling the tension in a Web ofsheet material from an unwind roll onto a winder roll driven by anelectric motor, comprising a controllable air brake on such unwind rollfor effecting tension in such web, a source of brake operating air underpressure, an air regulating valve connecting said source and said brakefor supplying air under regulated pressure to said brake and having areversible drive motor connected to increase and decrease the airpressure supplied by said valve, means for measuring the load on suchwinder motor and providing a signal thereof, servo means connected tooperate said reversible drive motor and responsive to said signal tovary the tension in said web, manual control means operable through saidreversible drive motor to set in a break-away tension independently ofsaid servo means, and automatic switch means connected to transfer thecontrol of said brake from said manual means to said servo means a fixedtime subsequent to the starting of the winder motor.

References Cited in the file of this patent UNITED STATES PATENTS2,233,015 Kassell et al Feb. 25, 1941 2,723,806 Carter Nov. 15, 19552,798,677 Nicholson July 9, 1957 2,838,253 Jacobsen June 10, 1958

